Installation for the electroslag remelting of consumable electrodes with modulated current

ABSTRACT

A device for improving the quality of the metal of ingots, produced by the method of electroslag remelting of consumable electrodes in cooled moulds, the amplitude of the alternating current of low frequency of the installation being modulated by means of various modulators series-connected in the primary or secondary circuit of a transformer feeding the electroslag remelting installation. The modulation of the amplitude of the alternating current of a frequency equal or close to the frequency of the oscillations of the liquid metal bath causes resonance oscillations of the metal bath, which cause refining of the structure of the crystallizing ingot, elimination of dendritic non-uniformity and a higher quality of the metal.

United States Patent et al. [451 Sept. 26, 1972 54] INSTALLATION FOR THE, 52] us. Cl ..l64/250,13/9,13/24 ELECTROSLAG REMELTING 0F 51 Int. Cl. ..B22d 27/02 CONSUMABLE ELECTRODES WITH MODULATED CURRENT [72] inventors: Boris Evgenievich Paton, ul.

Filed:

Katasjubinskogo, 11/13, kv, 21; Vladimir Konstantinovich Lebedev, ul. Engelsa, 25, kv. l2; Boris lzrailevich Medovar, bulver L. Ukrainki, 2, kv. 8; Jury Vadimovich Latash, Vozdukhoflatsky Prospekt, 81, kv.v 14; Nikolai Vasilievich Podola, Pushkinskaya ul., 8, kv. 12; Oleg Petrovich Bondarenko, Kreschatik l5, kv. 34, all of Kiev; Semen Abramovich Leibenzon, prosp. Lenina, 185, kv. 36, Zaporozhie; Gary Petrovich Kaganovsky, patrioticheskaya ul., 48, kv. 71, Zaporozhie; Vadim Filimonovich Smolyakov, pr. Lenina, 155, kv. 60, Zaporozhie; Konstantin Sergeevich Eltsov, ul. 40 letia Sovetskoi Ukrainy, 6, kv. 1, Zaporozhie; Georgy Kharitonovich Gabuer, prospekt Lenina, 228, kv. 17, Zaporozhie; Dmitry Fedorovich Gladky, prospekt Metallurgov, 3, kv. 33, Zaporozhie, all of USSR.

July 6, 1970 Appl. No.: $6,141

Related US. Application Data Continuation of Ser. No. 641,605, May 26, 1967, abandoned.

[58] Field of Search ..164/50, 52, 250, 252; 13/24, 13/12, 9, 9 ES; 219/482-484, 492; 321/1 6 [56] References Cited UNITED STATES PATENTS 1,968,576 7/1934 Suits ..l3/12 UX 1,997,644 4/1935 Long ..321/6 X 2,370,467 2/1945 Hopkins ..164/252 2,890,368 6/1959 Boron et a1. ..13/12 X 3,036,188 5/1962 Ditto ..219/492 3,041,438 6/1962 Lovegroove ..219/492 X 3,055,959 9/1962 Vaughan ..l3/24 X 3,186,043 6/1965 Murtland, Jr. et al. ..164/52 X 3,193,758 7/1965 Friedlander ..13/12 X 3,379,238 4/1968 Sieckman ..l64/52 X Primary Examiner-R. Spencer Annear Attorney-Waters, Roditi, Schwartz & Nissen 5 7] ABSTRACT A device for improving the quality of the metal of ingots, produced by the method of electroslag remelting of consumable electrodes in cooled moulds, the amplitude of the alternating current of low frequency of the installation being modulated by means of various modulators series-connected in the primary or secondary circuit of a transformer feeding the electroslag remelting installation. The modulation of the amplitude of the alternating current of a frequency equal or close to the frequency of the oscillations of the liquid metal bath causes resonance oscillations of the metal bath, which cause refining of the structure of the crystallizing ingot, elimination of dendritic nonuniformity and a higher quality of the metal.

14 Claims, 6 Drawing Figures MTENTEDSEPZS I972 SHEET 1 0F 3 FIB. 4

PATENTEU 3925 I97? 3 693, 700

sum 3 0r 3 INSTALLATION FOR THE ELECTROSLAG REMELTING OF CONSUMABLE ELECTRODES WITH MODULATED CURRENT This application is a continuation of copending application Ser. No. 641,605, filed May 26, 1967, now abandoned.

The present invention relates to installations for the electroslag remelting of consumable electrodes.

. It is intended to be utilized in electrometallurgy, and more particularly in the production of high-quality steels and alloys by using a method of electroslag remelting.

Known in the prior art are installations for the electroslag remelting of consumable electrodes with the use of an alternating current in a cooled mould (see the book, written by Medovar 8.1. and others, entitled Electroslag remelting, 1963, chapter II, Section 2.

Ingots, however, obtained in the existing plants, for example, ingots of austenitic steels and nickel-based alloys, have a coarse-grained structure with a fairly considerable development of the dendritic segregation. In particular, bearing and high-speed tool steels in large sections obtained from ingots to be melted in the existing installations, are of a low quality as to the structure and carbide string formation.

The existing methods of eliminating an increased non-uniformity, for example, a long heat treatment, homogenizing annealing of ingots, applicable to a steel produced by the electroslag remelting, have proved to be of a low efficiency. For this reason, when carrying into effect the electroslag remelting of a number of steel grades and alloys, it is required to provide such conditions of the ingot solidification which would prevent the formation of the dendritic segregation, especially carbide segregation during the electroslag remelting of steel of the carbide class.

An object of the present invention is to provide an installation for the electroslag remelting of consumable electrodes, which enables obtaining metal ingots with a minimum formation of strings and dendritic nonuniformity in the metal structure, and free from gaseous and non-metallic inclusions, while having a finegrained crystalline structure.

This is accomplished by modulating the amplitude of an alternating current of low frequency feeding the electroslag remelting furnace.

It is known that when an alternating current passes through the boundary between the liquid slag and the liquid metal, there arises, in conventional installations for electroslag remelting, an electrocapillary vibration of the surface of the network. Besides, the liquid metal bath is subjected to electrodynamic forces which, as compared to the frequency of the feeding network, act with double frequency.

In the proposed installation for electroslag remelting, the modulation of the amplitude of the alternating current at a frequency, equal or close to the natural frequency of oscillation of the liquid metal bath, causes the electrodynamic forces and electrocapillary vibration in the liquid bath change with the same frequency, thus causing resonant oscillation of the liquid metal bath, which reduces dendritic segregation in the crystallizing metal, refining of the structure of the ingot and elimination of horizontal and dendritic nonuniformity.

The essence of the invention consists in the fact that in the installation for the electroslag remelting of consumable electrodes with the use of an alternating current in a cooled mould, a means for modulating the amplitude of an alternating current of low frequency is connected in series with the alternating current source.

It is expedient that the source of alternating current should be made in the form of a transformer, while the means for modulating the amplitude of an alternating current of low frequency must be connected into the circuit of primary or secondary winding of the transformer.

The means for modulating the amplitude of the alternating current of low frequency may be made in the form of an ignitron interrupter.

The means for modulating the amplitude of the alternating current of low frequency can be made in the form of a saturation choke complete with an interrupter of its control current for varying the inductance of the working choke winding.

It is expedient that the means for modulating the amplitude of the alternating current of low frequency should be made in the form of a choke provided with a 5 movable yoke for varying the inductance of the secondary winding of the transformer.

Other objects and advantages of the present invention will become more fully apparent from a consideration of the following description of exemplaryembodiments thereof, taken in conjunction with the appended drawings, in which:

FIG. 1 is an elementary diagram of the installation, realized according to the present invention;

FIG. 2 is an electrical diagram of the installation complete with an ignitron interrupter, according to the present invention;

FIG. 3 is an electrical diagram of the installation complete with a saturation choke employed as a means for modulating the amplitude of the alternating current, according to the present invention;

FIG. 4 is an electrical diagram of the installation complete with an electromagnetic modulator, according to the present invention;

FIG. 5a represents a graph characteristic of the variation of the feeding current with time;

FIG. 5b is another embodiment showing the relation between the feeding current and time.

The installation for the electroslag remelting of consumable electrodes 1 (FIG. 1) in a cooled mould 2 comprises a source of alternating current in the form of a transformer 3 and a means 4 (4') for modulating the amplitude of the,alternating current of low frequency, connected into the primary or secondary winding of the feeding transformer 3.

The means 4 for modulating the amplitude of the alternating current of low frequency is essentially an ignitron interrupter, consisting or ignitrons 5, 6 (FIG. 2) connected in parallel in direction towards each other, elements 7, 8 of the grid shift and ignition, phase shifters 9 and a time relay 10. The ignitron interrupter is connected into the circuit of the primary winding 12 of the feeding transformer 3, which is shunted by a ballast resistor 13.

v The installation operates as follows.

The process of electroslag remelting is effected according to one of the existing methods; the ignitron inmould 2, the contacts 11 are opened, and a signal is supplied to the elements 7, 8 for igniting the ignitrons 5, 6 complete with a time relay 10, operating according to an automatic duty impulse-pause.

Depending upon the duties of electroslag remelting adopted, there are practicable two orders of operation of the ignitron interrupter. According to the first duty, the modulation of the alternating current of low frequency is effected by switching on and off the ignitrons 5, 6, while the second duty involves abrupt variations of the phase of ignition of ignitrons, providing for the alternation of impulses of current and pauses (FIG. a) or alternations of impulses of current with maximum and minimum values of the amplitude (5b). In order to exclude an additional magnetizing of the feeding transformer, the ignitrons are synchronously actuated with the network, while each impulse is composed of an even number of half periods.

FIG. 3 illustrates another embodiment of the installation, in which a device for modulating the amplitude of the alternating current of low frequency is a saturation choke 14, whose working winding is connected into the circuit of secondary winding 16 of the transformer 3. The winding 17 for controlling the saturation choke.

14 is connected through a rectifier l8 and contacts 19 of the time relay to an autotransformer 20.

When the contacts 19 are opened, the inductance of the working winding 15 is great, and almost the whole voltage, induced in the secondary winding 16 of the transformer 3, drops in the saturation choke 14. The current of the melting process is of an insignificant value.

After closing the contacts 19, the inductance of the saturation choke drastically drops, and a current, sufficient for heating the slag bath up to the temperature of melting of the electrode 1, beings to flow along the circuit choke mould."

The required depth of modulation of the main current is achieved by adjusting the current flowing in the control winding 17 to be actuated by the aid of the autotransformer 20.

The frequency of modulation is specified by the time of switching in and switching off of the contacts 19 of the time relay.

The modulation of the alternating current of a frequency equal or near the frequency of oscillations of the liquid metal bath, an account of the presence of electrocapillar vibrations on the boundary slag-metal and electrodynamic forces, is likely to cause the resonance oscillations of the liquid metal, bath, which contributes to the refining of the structure of the ingot being produced, a decrease in the non-uniformity of the structure of metal and a reduction in the extent of development therein of the dendritic segregation.

FIG. 4 illustrates another embodiment of a means for modulating the amplitude of the alternating current of low frequency. A choke 21 is connected into the circuit of secondary winding 16 of the transformer 3. The magnetic circuit of said choke is provided with a rotating yoke 23, connected to an electric motor 24. The

value of the gap and resistance of the magnetic circuit 22 vary depending upon the position of the yoke 23.

This results in a variation of the inductive resistance of the choke 21, and is likely to modulate the alternating current feeding the mould 2.

The installation, represented in FIGS. 3 and 4, operates similarly to that shown in FIG. 2.

Though the present invention is described in connection with its preferred embodiment, it is evident that there may be allowed variations and modifications thereof that do not depart from the idea and scope of the invention, which will be readily understood by those skilled in the art.

What is claimed is:

1. An electroslag remelting installation comprising a mold for receiving a bath of molten slag, means for positioning a consumable electrode in said mold for immersion in said bath of molten slag, alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold, and means, for

modulating the amplitude of said alternating current, a

operating at a predetermined frequency below the supplied frequency of said alternating current.

2. An electroslag remelting installation as recited in claim 1 wherein said alternating current supply means comprises a transformer having primary and secondary circuits, the means for modulating the amplitude of alternating current being connected in the primary circuit of said transformer.

3. An electroslag remelting installation as recited in claim 1 wherein said alternating current supply means comprises a transformer having primary and secondary circuits, the means for modulating the amplitude of alternating current being connected in the secondary circuit of the transformer.

4. An electroslag remelting installation as recited in claim 1 wherein said means for modulating the amplitude of the alternating current is an ignitron interrupter.

5. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; and means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current, said means for modulating the amplitude of said alternating current comprising a saturation choke with an interrupter of its control current for varying the inductance of the working windings of said choke.

6. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current; said alternating current supply means comprising a transformer having primary and secondary circuits; and said means for modulating the amplitude of said alternating current being connected in the secondary circuit of the transformer and comprising a choke with a movable yoke to vary the inductance of the secondary circuit of said alternating current supply means.

7. An electroslag remelting installation as recited in claim 1 wherein the depth of modulation of said alternating current is 100 percent whereby said alternating current is applied to said molten slag in the form of onoff alternating current impulses.

8. An electroslag remelting installation as recited in claim 1 wherein said means for modulating said alternating current varies the amplitude of said alternating current between predetermined high and low values greater than 0.

9. An electroslag remelting installation as recited in claim 1 wherein the frequency at which said alternating current is modulated is near the natural frequency of oscillation of said liquid metal bath formed in said mold.

10. An electroslag remelting installation as recited in claim 9 wherein said alternating current supply is a transformer.

11. An electroslag remelting installation as recited in claim 10 wherein said means for modulating the amplitude of said alternating current is connected into the primary or secondary winding circuits of said trans? former.

12. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; means, for

modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current and near the natural frequency of oscillation of said liquid metal bath formed in said mold; said alternating current supply means being a transformer having primary and secondary winding circuits; and said means for modulating the amplitude of said alternating current being a saturation choke, the working windings of said choke being connected into the secondary winding circuit of said transformer and the control winding of said choke connected to an autotransformer through a rectifier and a set of contacts, and wherein the amplitude of said alternating current is modulated by controlling the current in said control windings by means of said autotransformer.

13. An electroslag remelting installation as recited in claim 9 wherein said means for modulating the amplitude of said alternating current is an ignitron interrupter.

14. An electroslag remelting installation comprising a mold for receiving a bath of molten slag, means for positioning a consumable electrode in said mold for immersion in said bath of molten slag, alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold, and means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current, the operation of saidi stallai nresul 'n in he re elti of said electrode with minimum or mation 0T strifigs and dendritic nonuniformity in the metal ingot formed. 

1. An electroslag remelting installation comprising a mold for receiving a bath of molten slag, means for positioning a consumable electrode in said mold for immersion in said bath of molten slag, alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold, and means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current.
 2. An electroslag remelting installation as recited in claim 1 wherein said alternating current supply means comprises a transformer having primary and secondary circuits, the means for modulating the amplitude of alternating current being connected in the primary circuit of said transformer.
 3. An electroslag remelting installation as recited in claim 1 wherein said alternating current supply means comprises a transformer having primary and secondary circuits, the means for modulating the amplitude of alternating current being connected in the secondary circuit of the transformer.
 4. An electroslag remelting installation as recited in claim 1 wherein said means for modulating the amplitude of the alternating current is an ignitron interrupter.
 5. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; and means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current, said means for modulating the amplitude of said alternating current comprising a saturation choke with an interrupter of its control current for varying the inductance of the working windings of said choke.
 6. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current; said alternating current supply means comprising a transformer having primary and secondary circuits; and said means for modulating the amplitude of said alternating current being connected in the secondary circuit of the transformer and comprising a choke with a movable yoke to vary the inductance of the secondary circuit of said alternating current supply means.
 7. An electroslag remelting installation as recited in claim 1 wherein the depth of modulation of said alternating current is 100 percent whereby said alternating current is applied to said Molten slag in the form of on-off alternating current impulses.
 8. An electroslag remelting installation as recited in claim 1 wherein said means for modulating said alternating current varies the amplitude of said alternating current between predetermined high and low values greater than
 0. 9. An electroslag remelting installation as recited in claim 1 wherein the frequency at which said alternating current is modulated is near the natural frequency of oscillation of said liquid metal bath formed in said mold.
 10. An electroslag remelting installation as recited in claim 9 wherein said alternating current supply is a transformer.
 11. An electroslag remelting installation as recited in claim 10 wherein said means for modulating the amplitude of said alternating current is connected into the primary or secondary winding circuits of said transformer.
 12. An electroslag remelting installation comprising: a mold for receiving a bath of molten slag; means for positioning a consumable electrode in said mold for immersion in said bath of molten slag; alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold; means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current and near the natural frequency of oscillation of said liquid metal bath formed in said mold; said alternating current supply means being a transformer having primary and secondary winding circuits; and said means for modulating the amplitude of said alternating current being a saturation choke, the working windings of said choke being connected into the secondary winding circuit of said transformer and the control winding of said choke connected to an autotransformer through a rectifier and a set of contacts, and wherein the amplitude of said alternating current is modulated by controlling the current in said control windings by means of said autotransformer.
 13. An electroslag remelting installation as recited in claim 9 wherein said means for modulating the amplitude of said alternating current is an ignitron interrupter.
 14. An electroslag remelting installation comprising a mold for receiving a bath of molten slag, means for positioning a consumable electrode in said mold for immersion in said bath of molten slag, alternating current supply means for passing alternating current through said electrode into said bath of molten slag, whereby a liquid metal bath is formed in said mold, and means, for modulating the amplitude of said alternating current, operating at a predetermined frequency below the supplied frequency of said alternating current, the operation of said installation resulting in the remelting of said electrode with minimum formation of strings and dendritic nonuniformity in the metal ingot formed. 